1. Field of the Invention
The present invention relates to a bent zoom lens used in an imaging apparatus.
2. Description of the Related Art
Recently, it is demanded to further downsize a compact imaging apparatus such as a digital still camera and a video camera. Accordingly, it is demanded to downsize an imaging lens, particularly a zoom lens, to be installed in a compact imaging apparatus. Particularly, it is demanded for a zoom lens installed in a digital still camera to have an angle of view of 70 degrees or wider at a wide-angle end. In addition, it is demanded to improve an optical performance of an imaging lens corresponding to improved pixel resolution of an imaging device to be installed in a compact imaging-apparatus.
To meet such demands, a rear-focus zoom lens has been proposed that is configured to focus by shifting lens groups other than a first lens group arranged at a position closest to an object (for example, Japanese Patent No. 3486474).
In the above rear-focus zoom lens, an entire lens system is downsized relatively easily, while obtaining an image-formation property suitable for a solid-state imaging device having many pixels. However, the optical path is constituted in a rectilinear configuration, thereby limiting length of the lens system to be shortened.
As such, a zoom lens has been proposed to further shorten a total length of a lens system, which zoom lens is configured to include a prism arranged in an optical path from a first lens group to an image surface to bend the optical path midway (for example, Japanese Patent Application Laid-Open No. 2004-354869).
The above zoom lens having the prism is configured to adopt an up-and-down direction or right-and-left direction as a movable direction of lenses upon changing a magnification to eliminate protruded portions or protruded movable portions upon imaging, and configured to downsize the first lens group having the prism to thereby realize further downsizing with reduction in thickness. However, when an image-formation magnification of a fifth lens group is increased to downsize the lens system, an image is considerably deteriorated only by a slight deviation of a fourth lens group as a focus group from a focusing position. This has resulted in such a problem that an image-formation quality is hardly maintained, due to occurrence of a cause (like a manufacturing error) that disables precise alignment of the focus group with the focusing position.